CN109506806B - Method for simultaneously measuring internal temperature and thickness of high-temperature structure under transient condition - Google Patents
Method for simultaneously measuring internal temperature and thickness of high-temperature structure under transient condition Download PDFInfo
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- CN109506806B CN109506806B CN201811414927.4A CN201811414927A CN109506806B CN 109506806 B CN109506806 B CN 109506806B CN 201811414927 A CN201811414927 A CN 201811414927A CN 109506806 B CN109506806 B CN 109506806B
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01K—MEASURING TEMPERATURE; MEASURING QUANTITY OF HEAT; THERMALLY-SENSITIVE ELEMENTS NOT OTHERWISE PROVIDED FOR
- G01K11/00—Measuring temperature based upon physical or chemical changes not covered by groups G01K3/00, G01K5/00, G01K7/00 or G01K9/00
- G01K11/22—Measuring temperature based upon physical or chemical changes not covered by groups G01K3/00, G01K5/00, G01K7/00 or G01K9/00 using measurement of acoustic effects
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01B—MEASURING LENGTH, THICKNESS OR SIMILAR LINEAR DIMENSIONS; MEASURING ANGLES; MEASURING AREAS; MEASURING IRREGULARITIES OF SURFACES OR CONTOURS
- G01B17/00—Measuring arrangements characterised by the use of infrasonic, sonic or ultrasonic vibrations
- G01B17/02—Measuring arrangements characterised by the use of infrasonic, sonic or ultrasonic vibrations for measuring thickness
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Abstract
The invention discloses a method for simultaneously measuring the internal temperature and thickness of a high-temperature structure under a transient condition, which solves the problem that the internal temperature and thickness of the structure cannot be simultaneously measured under the transient condition. According to the method, the simultaneous measurement of the structure thickness and the internal temperature is converted into a multi-parameter identification problem of the thermal boundary condition and the structure thickness of the heat conduction problem according to the medium temperature-ultrasonic propagation characteristic. The ultrasonic propagation time under the transient heat transfer condition is obtained by adopting an ultrasonic echo method, and the related internal temperature and thickness of the structure can be rapidly, nondestructively and contactlessly measured by solving the inverse problem of heat conduction. The method is suitable for simultaneously measuring the thickness and the internal temperature of the relevant structures of high-temperature equipment such as high-temperature boilers, pipelines, molds and the like under the transient heat transfer condition.
Description
Technical Field
The invention belongs to the technical field of ultrasonic detection, and particularly relates to a method for simultaneously measuring the internal temperature and thickness of a high-temperature structure under a transient condition.
Background
Ultrasonic thickness measurement is one of the most common nondestructive testing methods, and has been widely applied in the fields of petroleum, chemical industry, machinery, metallurgy, electric power, ships and the like. With the increasing and more complex high-temperature scientific experiments and engineering applications, the precision requirement on high-temperature thickness measurement, particularly high-temperature fixed-point thickness measurement, is higher and higher. Compared with normal temperature thickness measurement, the difficulty of high temperature thickness measurement is that the sound velocity on the ultrasonic propagation path is changed due to the gradient change of the non-uniform temperature field in the measured structure. Therefore, the traditional thickness measurement method adopting the temperature coefficient compensation method has the problems that: firstly, the temperature of a measured structure needs to be given in advance, and then the measured data is corrected according to the relationship between the temperature and the sound velocity; secondly, due to the gradient change of the temperature field, a great model error is probably caused by only correcting according to a certain single temperature value. Meanwhile, the temperature measurement technology based on the ultrasonic method can realize nondestructive detection of the steady state/transient state temperature field in the structure, and can meet the requirements of accurate temperature measurement and online control in industrial production and scientific research. However, it is generally assumed in these thermometry studies that the wall thickness (i.e., the distance of ultrasound propagation) is known. Obviously, most of the existing studies assume temperature and predict wall thickness, or fix wall thickness and predict temperature, both of which are generally unknown in engineering practice. Therefore, the ultrasonic measurement method for simultaneously predicting the structure temperature and the structure thickness has higher engineering practical value.
Disclosure of Invention
The invention aims to provide a method for simultaneously measuring the internal temperature and the thickness of a high-temperature structure under a transient condition. According to the medium temperature-ultrasonic propagation characteristic, an ultrasonic echo method is adopted to obtain the ultrasonic propagation time under the transient heat transfer condition, and the related internal temperature and thickness of the structure can be rapidly, nondestructively and contactlessly measured by solving the inverse problem of heat conduction. The method is suitable for simultaneously measuring the thickness and the internal temperature of the relevant structures of high-temperature equipment such as high-temperature boilers, pipelines, molds and the like under the transient heat transfer condition.
In order to achieve the purpose, the invention is mainly realized by the following technical scheme:
sampling a tested structure, and measuring the relation between the ultrasonic propagation speed V and the medium temperature T through experiments;
step two, obtaining the measured structure at t by an ultrasonic pulse echo methodiTime of ultrasonic wave propagation time ttof,m；
Step three, based on the ultrasonic echo signal, the simultaneous measurement of the structure thickness and the internal temperature is converted into a multi-parameter identification problem of the thermal boundary condition and the structure thickness of the heat conduction problem, and the following objective function is adopted:
in the formula: q is a thermal boundary condition, L is the distance of the ultrasonic wave propagating in the solid medium in a single direction, namely L is the thickness of the detected structure, and ttof,i,cFor the calculated ultrasonic wave propagation time, subscript i represents the measurement time sequence, n represents the number of sampling points, and V is the propagation speed of the acoustic wave in the solid medium;
the constraint conditions are as follows:
in the formula: k is the thermal conductivity of the material, CpIs the specific heat of the material, and rho is the density of the material;
step four, solving the inverse problem of heat conduction to obtain the internal temperature field of the measured structure,
the solving process is as follows:
(1) setting an initial value of a parameter;
(2) solving a state equation by numerical values, and solving the values of a temperature field T (x, T) and an objective function J, wherein x is the position in the thickness direction of the structure;
(3) solving a sensitivity equation by numerical values to obtain a sensitivity vector;
(4) optimizing the parameter value by adopting a Hooke-Jeeves method or other gradient optimization methods to obtain q and L;
(5) judging whether convergence is achieved (taking epsilon to be less than or equal to 1e-6), and stopping calculation if convergence is achieved; otherwise, returning to the step (2) to repeat iteration until reaching the convergence criterion;
(6) based on the positive heat conduction problem calculation, a temperature field T (x, T) in the structure to be measured is obtained.
In the above solution, the thermal boundary condition is expressed in the heat transfer model as a piecewise function varying with time.
In summary, due to the adoption of the technical scheme, the invention has the beneficial effects that:
based on the multi-parameter identification technology, the non-uniform temperature field and the wall thickness (structural thickness) in the structure such as the furnace wall of the blast furnace, the high-temperature steam pipeline and the mold can be measured simultaneously, the accuracy of the high-temperature fixed-point thickness measurement is effectively improved, and the application range of the ultrasonic detection technology is greatly widened.
The equivalent thermal boundary condition is expressed as a segmented functional expression changing along with time, so that the limitation conditions of a functional relation expression of the thermal boundary condition along with the measurement time or prior information and the like are avoided being required to be given in advance, and the method has important engineering practical value.
Drawings
FIG. 1 is a comparison of ultrasonic probe values for varying temperature thermal boundary conditions with thermocouple measurements.
FIG. 2 is a comparison of ultrasonic probe values and thermocouple measurement values of the temperature distribution within the test piece.
Detailed Description
In order to make the objects, technical solutions and advantages of the present invention more clearly apparent, the following description is made with reference to the accompanying drawings and embodiments
The present invention will be described in further detail. It should be understood that the specific embodiments described herein are merely illustrative of the invention and are not intended to limit the invention.
A cylindrical 20# steel material test piece is adopted in the experiment. The thickness of the test piece was measured with a vernier caliper, and the average value was taken 5 times and found to be 50.01 mm. The bottom of the test piece is measured to be in contact with a flat heater so as to heat the test piece under the temperature condition changing along with the time (variable temperature heating), and the total time length is 300 s. An electromagnetic ultrasound probe is placed on top of the test piece, exciting/receiving the signal once every 1 s. Meanwhile, in order to verify the accuracy of the temperature field in the ultrasonic measurement structure, staggered punching (the interval in the thickness direction is about 5mm, and the ring direction is 45 degrees) is carried out on the surface of the test piece, and thermocouples are installed for temperature measurement. And the periphery of the test piece is wrapped by a heat insulation material, so that the temperature field in the test piece is kept in a one-dimensional state as far as possible.
The thermal boundary model using the piecewise functions of 4, 5 and 6 respectively is used to simultaneously perform the heating boundary and the specimen thickness (the distance of the ultrasonic wave propagating in one direction), wherein the predicted results of the specimen thickness are 49.27mm, 50.00mm and 49.99mm respectively, and the predicted results of the heating boundary are shown in fig. 1, and the initially input thermal boundary conditions are q (t) 26 ℃. Meanwhile, fig. 2 compares the temperature change inside the structure with time based on the ultrasonic method 6 segmented thermal boundary model and on the thermocouple measurement.
Research on different segmented models shows that ultrasonic detection can effectively measure the thickness of the structure and the temperature field distribution of internal transient states of the structure at the same time, wherein errors of 4, 5 and 6 segmented models in thickness measurement are respectively 1.48%, 0.02% and 0.04%, and prediction errors of thermal boundaries (compared with temperature values corresponding to the central points of each segment) are respectively 2.44%, 4.66% and 4.24%. In practical application, from the viewpoint of both precision and efficiency, 4 segmented models can be selected.
The above description is only for the purpose of illustrating the preferred embodiments of the present invention and is not to be construed as limiting the invention, and any modifications, equivalents and improvements made within the spirit and principle of the present invention are intended to be included within the scope of the present invention.
Claims (2)
1. A method for simultaneously measuring the internal temperature and thickness of a high-temperature structure under transient conditions is characterized by comprising the following steps:
sampling a tested structure, and measuring the relation between the ultrasonic propagation speed V and the medium temperature T through experiments;
step two, obtaining the ultrasonic wave propagation time t of the measured structure at the time ti through an ultrasonic pulse echo methodtof,m；
Step three, based on the ultrasonic echo signal, the simultaneous measurement of the structure thickness and the internal temperature is converted into a multi-parameter identification problem of the thermal boundary condition and the structure thickness of the heat conduction problem, and the following objective function is adopted:
in the formula: q is a thermal boundary condition, L is the distance of the ultrasonic wave propagating in the solid medium in a single direction, namely L is the thickness of the detected structure, and ttof,i,cFor the calculated ultrasonic wave propagation time, subscript i represents the measurement time sequence, n represents the number of sampling points, and V is the propagation speed of the acoustic wave in the solid medium;
the constraint conditions are as follows:
in the formula: k is the thermal conductivity of the material, CpIs the specific heat of the material, and rho is the density of the material;
step four, solving the inverse problem of heat conduction to obtain the internal temperature field of the measured structure,
the solving process is as follows:
(1) setting an initial value of a parameter;
(2) solving a state equation by numerical values, and solving the values of a temperature field T (x, T) and an objective function J, wherein x is the position in the thickness direction of the structure;
(3) solving a sensitivity equation by numerical values to obtain a sensitivity vector;
(4) optimizing the parameter value by adopting a Hooke-Jeeves method or other gradient optimization methods to obtain q and L;
(5) judging whether the convergence is carried out, taking epsilon to be less than or equal to 1e-6, and stopping calculation if the convergence is carried out; otherwise, returning to the step (2) to repeat iteration until reaching the convergence criterion;
(6) based on the positive heat conduction problem calculation, a temperature field T (x, T) in the structure to be measured is obtained.
2. The method of claim 1, wherein the method comprises measuring the temperature and thickness of the inside of the high-temperature structure under transient conditions,
characterized in that the thermal boundary conditions are represented in the heat transfer model as a piecewise function over time.
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